[ceph-users] Clarification of documentation

In the docs: https://docs.ceph.com/docs/master/radosgw/multisite/ - in the section Requirements and Assumptions There is this warning hint: "Running a single Ceph storage cluster is NOT recommended unless you have low latency WAN connections." What exactly does "single Ceph storage cluster" mean? * Just having one site? * Do I need to run multiple independent clusters across a number of n sites before I can do multi-site - so it would not be possible to start with one site and add further sites step by step? And what exactly happens with higher latency WAN connections?